Flame monitor system and method using multiple radiation sensors

ABSTRACT

A flame monitor method and system where one pair or more of radiation sensors respond to high frequency radiation fluctuations in regions of the same flame or different flames, with each sensor producing an electrical signal indicative of the flame condition. The electrical signals developed by the sensors are utilized by an associated electrical circuit which produces an output signal which is a function of the difference in signals of the individual sensors of each sensor pair or the sum of the outputs of the sensor pairs used. Filtering, amplifying, rectifying, and calibrating means are included in the circuit to provide an output signal capable of any or all of the functions of indicating, controlling the flame condition and actuating an alarm.

United States Patent Wheeler 1 Sept. 5, 1972 [54] FLAME MONITOR SYSTEMAND METHOD USING MULTIPLE RADIATION SENSORS [72] Inventor: Peter JohnWheeler, Carshalton Beeches, England [73] Assignee: Bailey Miters &Controls Limited, Surrey, England [22] Filed: Feb. 1, 1971 [21]App1.N0.: 111,589

[52] US. Cl. ..250/217 F, 340/228.2 [51] Int. Cl. ..G08b 21/00 [58]Field of Search ..250/217 F, 215, 210; 340/2282, 228.1; 431/79, DIG. 43

[56] References Cited UNITED STATES PATENTS 2,820,945 1/1958 Marsden, Jr..340/228.2 2,306,073 12/ 1942 Metcalf ..250/217 F X Doubek, Jr. et a1...250/210 2,388,124 10/1945 Crews ..250/217 F X Primary Examiner-WalterStolwein Attorney-Joseph M. Maguire [57] ABSTRACT A flame monitor methodand system where one pair or more of radiation sensors respond to highfrequency radiation fluctuations in regions of the same flame ordifferent flames, with each sensor producing an electrical signalindicative of the flame condition. The electrical signals developed bythe sensors are utilized by an associated electrical circuit whichproduces an output signal which is a function of the difference in Ysignals of the individual sensors of each sensor pair or the sum of theoutputs of the sensor pairs used. Filtering, amplifying, rectifying, andcalibrating means are included in the circuit to provide an outputsignal capable of any or all of the functions of indicating, controllingthe flame condition and actuating an alarm.

11 Claims, 6 Drawing Figures PATENTEDsEP 51972 3.689.773v

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, F BY PETER J. WHEELER ATTORNEY BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates generally to methods andsystems for flame monitoring of a burner in a furnace and morespecifically to an apparatus utilizing at least one pair of radiationsensors to monitor a flame exhibiting high frequency radiationfluctuations. Circuit means is connected to the sensors to produce anoutput signal that will be the sum of the outputs of each pair ofsensors, where each pair of sensors produces an output signal that isthe difference of individual signal outputs of the pair.

2. Description of the Prior Art Flame monitoring of a burner hasheretofore comprised the use of thermocouples, expansion tubes, andradiation sensors. Due to the extremely high flame temperatures inprocess boilers, monitoring of boiler flames in large furnaces has beendone mainly with remotely located radiation sensors or sonic microphonepickups, which detect the frequency of the flame.

Although the radiation sensor circumvents the problem of placing asensor in the region of high flame temperature, is has shortcomings suchas the inability to differentiate between flame radiation and radiationfrom the heated boiler or furnace wall regions. Thus, the flame may beextinguished and the flame detector will fail to respond. The fuelsupply to the burners will continue to be discharged onto the hotfurnace walls. This time lag between loss of flame and shut down of thefuel supply can cause an explosion.

There are specialized radiation sensors which sense ultravioletradiation and others which generate signals corresponding to theamplitude of the high frequency flicker of the flame monitored. Bothtypes of sensors can distinguish between flame radiation and backgroundradiation since both ultraviolet and flickering radiation find a sourceof excitation exclusively in the flame. The use of a flickering typeradiation sensor produces an output signal that is continuouslyfluctuating. The fluctuation may be hard to distinguish, and the problembecomes one of accurate detection of this fluctuation.

This problem of detecting a small variation in sensor output iseffectively solved by the applicants invention in the following manner.Two sensors are positioned to converge and the radiation magnitudereceived by the individual sensors is similar. A circuit means subtractsthe output signals of the individual sensors of the pair, the steady andslowly varying components of flame radiation from the flame areeffectively canceled leaving the rapidly varying difference signal forflame detection. The high frequency flame flickering is due to randompulses or burst of radiation from very localized sources in the flame,and there will always be a residual, varying component from the dualsensor system as long as the flame is present.

SUMMARY OF THE INVENTION A flame monitor method including the steps ofsimultaneously sensing radiation from two parts of a flame regionexhibiting high frequency radiation and combining the radiation fromthese two parts so as to cancel identical radiation components andretain the nonidentical components. The retained non-identical radiationcomponents are modified to provide a control signal suitable foractuating flame monitor equipment.

One flame monitor system utilizing the above described method accordingto the invention comprises at least one pair of radiation sensors, tomonitor a flame exhibiting high radiation fluctuations. The output ofeach sensor is connected so as to give an output signal from the pairconsisting of only the varying difference Another flame monitor system,in accordance with the invention, is comprised of a pair or numerouspairs of radiation sensors and circuit means connected thereto with thecircuit output of each pair of sensors comprising only the varyingdifference component of the signals from each sensor pair. The circuithas means for balancing the steady state outputs of the individualsensors of each pair so that a null output may be obtained when eachsensor of the pair is subjected to identical non-flickering radiation.The circuit further has filtering, amplifying, and rectifying means tomodify the output of the sensor pair or pairs to a form capable ofproviding alarm, indication, and control functions.

The sensors are enclosed within a housing either individually or inpairs with a lens or lenses located on the enclosure face sighting onthe flame to focus the radiation to the appropriate sensor. The sensorelements are either photovoltaic or photo-resistive. Photovoltaicsensors are electrically series connected while photoresistive sensorsare electrically parallel connected in the associated circuit means.

Further in accordance with the invention flame monitoring systems usingthe above method include a plurality of radiation sensing pairs, witheach pair sensing different regions of a flame. The output of theindividual pairs is combined additively and modified to provide acontrol signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side elevationthrough a pulverized coal burner arranged in a furnace wall throughwhich extend the sighting tubes of a flame monitoring system.

FIG. 2 is a plan view of a flame monitoring system showing theconvergence of the sighting assembly.

FIG. 3 is a sectional plan view of a common sighting head mounting apair of sensors and a common lens.

FIG. 4 is a circuit schematic of the invention showing a pair ofphotovoltaic sensors connected in'series opposition.

FIG. 4a is a circuit schematic of the invention showing a pair ofphoto-resistive sensors connected in parallel.

FIG. 5 is a schematic of a plurality of sensor pairs set to view a highfrequency radiation zone of a flame and electrically interconnected soas to produce an output signal which is the sum of the signal differenceof each pair.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularlyto the drawings wherein the showings are for purposes of illustratingthe preferred embodiments of the invention and not for purposes oflimiting same, FIG. 1 shows a pulverized coal burner 32 arranged at avertical wall 1 of a furnace for discharging through a port 2, in thewall, a combustible mixture of pulverized coal and air.

The burner is of a kind with frusto-conical casing 3, coaxial with theport, which extends toward the furnace from a chamber 4. A feed pipe 5connects with the chamber 4 so that a stream of a mixture of pulverizedcoal with air is supplied through the pipe 5. The mixture whirls aboutthe axis of the casing 3 and is discharged from the open end thereof.Arranged coaxially with the casing 3 is an inner frusto-conical casing 6which supplies a stream of additional air to the central region of thewhirling mixture discharged from the casing 3.

The burner 32 is mounted in a wall 7 exterior to the furnace, and thewall 7 acts in conjunction with the furnace wall 1 to .define a windboxor plenum chamber 8, common to a plurality of burners. The chamber 8supplies the remainder of the air necessary for the efiicient combustionofthe pulverized coal. This added air flows to the port 2 through an airregister 9, which comprises an annular casing extending aroundthefrusto-conical casing 3 at the face of the wall 1. The peripheral wall 11 of the register 9 is formed as a plurality of inclined vanes orlouvers (not shown) which causes the air flow from the plenum chamber towhirl around the burner axis. Means (not shown) are provided foradjusting simultaneously the inclination of all the said vanes in orderto regulate the air flow as is well known to those in the art. In orderto ignite the flame, an electrical igniter 13, positioned in the furnaceend of the burner, is operated after projecting it towards the furnacefrom which it is withdrawn when the flame is started.

When the pulverized coal and the combustion air are discharged into thefurnace, some coal particles ignite relatively early in the flame andsome late. The fluent mass from the burner, initially consists ofunignited coal particles and air and then of pulverized coal with anincreasing portion of the ignited particles and the gaseous combustionproducts in air. The radial extent of the mass increases in diameter, sothat it may be con sidered to have a definite boundary, with distancefrom the burner, for example, in approximately conical shape asindicated by the interrupted lines 15. Reference line 17 denotes theearlier zone downstream of which the fluent mass appears as an intenselyradiant flame, the flame front upstream of the zone 17 is less brilliantbecause, the proportion of coal particles which have been ignited issmaller and the proportion of radiation obscured by unignited coalparticles is larger.

Located above the burner 32 and extending through the wall 7, the plenumchamber 8 and the furnace wall 1 are two sighting tubes 42 and 44 of aflame monitoring system. The first sensor sighting tube 42 leads to asensor assembly comprising a housing 22 having a focusing lens 18 on theend facing the flame 34. Located internally to the housing 22 is asensor 14 located at the end opposite the lens 18.

The second sensor sighting tube 44 leads to a sensor assembly 12 shownproximate to the first sensor assembly 10. The assembly 12 has a housing24 with a focusing lens 20 on the end facing the flame 34 and a sensor16 internal to the housing 24 at the end opposite the lens 20.

A common sensor leadwire 26 connects leads of the same polarity fromsensor 14, 16, and second sensor leadwires 28, 30 are used to connectthe sensor to an electrical circuit. This connection provides a serieselectrical connection of sensors 14, 16.

The flame 34 originating from the burner 32 has a flame front exhibitinghigh frequency flickering radiation 40 within which is located a firstsighting area 36 and a second sighting area 38 as viewed by the firstand second sensors 14, 16 respectively.

In operation the sensors 14, 16 produce an electrical output signalwhich is a function of the flame radiation. As the flame radiationflickers, so does the output signal. The sensors are connected seriesopposing in polarity to produce an output signal at the terminals ofleadwires 28, 30 from which the steady state and slowly varyingcomponents have been cancelled by the circuit leaving only the varyingdifference components. If the flame 34 were extinguished, the sensors14, 16 would immediately sense only a steady state residual radiationfrom the surroundings and produce a zero output difference signalindicating the lack of flame.

Referring now to FIG. '2, there is schematically shown a flamemonitoring system including electrical circuit means for producing anoutput signal which is a function of the difference between the signalsfrom the first-and second radiation sensing assemblies 10, 12. Thesensor sighting tube 42 leads to a lens 18, and the second sensorsighting tube 44 leads to the lens 20. The sighting tubes 42, 44 isolatethe sighting areas 36, 38 respectively and prevent any radiation fromone sighting area from affecting any sensor except the one associatedwith it. Further the tube allows the placement of the sensor assembly ina location of cooler ambients removed from the heat of the flame 34.

The output of the dual sensor assemblies is connected to an A.C.amplifier 46 through an RC coupling consisting of a resistor 29 and acapacitor 27. By reason of this RC coupling, low frequency variationsare attenuated so that the input to the amplifier 46 consists mainly ofhigh frequency variations. The flame front 40 produces radiation withhigh frequency flicker. It is found that in spite of the connection ofthe cells in opposition, the amplifier 46 receives an oscillatory input.This is explainable by the fact that high frequency flicker in theradiation from the region 40 is due to random pulses or bursts ofradiation from varying numerous, localized sources of radiation. Sincethe majority of the individual pulses occurring in either part of theflame region will, in view of their random timing, not be synchronouswith any of the pulses occurring in the other part of the flame regionand therefore their effect will appear in the input to the amplifier.The amplifier 46 provides a means of raising the output signal from theRC coupling consisting of this high frequency variation to a levelcapable of performing the desired indication, alarm, or control functionat the amplifier output leads 48. The signal from leads 48 inputs into arectifier 47 which is either a full wave or a half wave rectifier. Thefunction of the rectifier 47 is to produce a steady D.C. output at therectifier output leads 49.

Referring now to FIG. 3, a sensor pair housing 50 is shown having a lens52 mounted near one end of the housing 50. First and second sensors 14',16 are shown mounted internal to the housing 50 on a mounting block 51located at the end of the housing 50 opposite the lens 52. A partition53 separates the first sensor 14' from the second sensor 16'. Sensorleadwires are connected to the first and second sensors 14', 16'.

This housing arrangement may be used when the sensors are viewingclosely adjacent flame sighting areas. It

should be understood that with this housing arrangement, the partition53 and the lens 52 are arranged so as to insure that sensor 14 receivesradiation from a flame area which is not radiated to the sensor 16' andvice versa. The same effect may be had exclusively with lensingassemblies or with other partitioning configurations.

Referring now to FIG. 4, a first photovoltaic sensor 55 is shown havingits negative terminal connected to the negative terminal of a secondphotovoltaic sensor 57 through common leadwire 26. The positive terminalof the first sensor 55 is connected to one terminal of a potentiometerR1 whose other terminal joins the common leadwire 26 and a potentiometerR2. The positive terminal of the second sensor 57 is connected to thepotentiometer R2. An RC coupling consisting of capacitor 27 and resistor29 connects with the sensors through leadwires 54, 56 to provide theinput to amplifier 46. The amplifier is connected to a rectifier 47through leads 48. The rectifier has leads 49 which provide a steady D.C.output from this photovoltaic assembly as described previously inreference to FIG. 2.

The effect of this circuit arrangement is to place the first and secondphotovoltaic sensors 55, 57 in series opposition through potentiometersR1, R2 respectively. These same potentiometers are also used tocalibrate the sensors so that steady and slowly varying components offlame radiation would be cancelled. Calibration is performed bysubjecting the first and second sensors 55, 57 to identicalnon-flickering radiation. The first and second sensors 55, 57 thenproduce their respective voltages across potentiometers R1 and R2. Theportion of the voltage across the potentiometer R1 between the commonleadwire 26 and potentiometer R1 leadwire 54 is in series oppositionwith the portion of the voltage across the potentiometer R2 between thecommon leadwire 26 and potentiometer leadwire 56. Thus a zero inputlevel to the amplifier 46 may be produced by adjusting one or both ofthe potentiometers until the opposing voltages are equal. In actualoperation when the sensors are detecting flickering radiation, likecomponents of the first and second sensor 55, 57 outputs will cancelleaving only the flickering radiation components of the flame. Theseflickering components are inputed to the amplifier 46 through the RCcoupler which attenuates the slowly varying components. The amplifier 46on raising the signal level of the high frequency radiation input, willinput this elevated signal to the rectifier 47 which will, in turn,convert this elevated signal to a pure D.C. output at the rectifier 47output leads 49.

Referring now to FIG. 4a, a Wheatstone bridge sensor arrangement isshown using a first photo-resistive sensor 62 and a secondphoto-resistive sensor 64 located on separate branches of the bridge. Apotentiometer R3 is connected in parallel with the sensors acrossopposite corners to complete the bridge. The bridge is powered throughleads 61 with the bridge output connected to the amplifier 46 by leads58 and 60 through the RC coupler consisting of capacitor 27 and resistor29. The amplifier 46 in turn is connected to the rectifier 47. Thiscircuit arrangement results in a pure D.C. output as explainedpreviously in reference to jacent branches until the ratio of thisresistance split is equal to the ratio of the resistance of the firstand second photo-resistive sensors 62, 64. This is done with anidentical source of non-flickering radiation applied to both the firstand second sensors 62, 64. When the sensors are then subjected tonon-identical flickering radiation, the bridge balance will be destroyedand an output signal from the bridge will be transmitted to theamplifier 46. The amplifier raises the signal to a level capable ofproviding control, alarm, or indication. The oscillatory, elevatedamplifier signal is inputed to the rectifier 47 which converts thissignal to a D.C. output at the rectifier leads 49.

Referring now to FIG. 5, an alternative arrangement is shown using twopairs of sensors, each individual pair the same as described inreference to FIG. 2. This same concept can be carried out to include theuse of more than two pairs of sensors just as easily. A first sensorpair assembly 66 and a second sensor pair assembly 68 are shown sightinga first area 70 and a second area 72 respectively. Both the first andsecond viewing areas 70, 72 have individual sensor viewing areas 84, 86respectively.

Both the first and second sensor pair assemblies 66, 68-have theirindividual sensors connected in opposition through a first commonleadwire 74 and a second common leadwire 76. The two remaining leadsfrom the first sensor pair assembly, input lead 82 and an output lead78, connect the first sensor pair 66 in series with the second sensorpair 68. The amplifier input lead is also connected to the second sensorpair assembly 68. A shunt resistor 29 is applied across the input to theamplifier 46 and with a capacitor 27 forms the RC coupler for lowfrequency attenuation. The amplifier is connected to the rectifier 47which provides a steady D.C. output signal at the rectifier leads 49.

In operation this circuit provides for series opposition of theindividual sensor outputs of both the first and second sensor pairs andseries addition of the first and second sensor pair outputs. Thiscombined signal is then inputed to the amplifier 46 through the RCcoupler with the amplifier raising the high frequency signal to a levelcapable of indicating or controlling the flame 34 or sounding an alarmcondition in case of flame failure. Because the signal is stilloscillatory, however, it is inputed to the rectifier 47 which produces asteady D.C. output at the rectifier leads 49.

Certain modifications will be obvious to persons skilled in the art uponreading the specification. It is intended to include not only the matteras specified but also these obvious modifications.

What I claim as new and desire to secure .by Letters Patent of theUnited States is:

1 A flame monitoring system comprising: first means, aligned to sensethe radiation from a region of the flame exhibiting high frequencyrandom flickering radiation components and other radiation components,for producing a first electrical signal indicative thereof; secondmeans, aligned to sense radiation from another part of said region ofthe flame exhibiting high frequency random flickering radiationcomponents and other radiation components, for producing a secondelectrical signal indicative thereof; and,

electrical circuit means for combining said first and said secondelectrical signals to cancel the other radiation components of saidsignals and retain the random high frequency flickering radiationcomponents of the signals proportional to the sensed radiation.

2. A flame monitoring system as set forth in claim 1 wherein saidelectrical circuit includes;

filtering, amplifying, and rectifying means for modifying the outputsignal of said electrical circuit means to a form capable of controllingsaid flame.

3. A flame monitoring system as set forth in claim 2 wherein said firstand second radiation sensing means are photovoltaic cells and areconnected in series opposition in said electrical circuit.

4. A flame monitoring system as set forth in claim 2 where said firstand second radiation sensing means are photoresistive cells and areconnected in parallel on individual arms of a Wheatstone bridge in saidelectrical circuit means.

5. A flame monitoring system as set forth in claim 1, wherein saidelectrical circuit means includes means for balancing the outputs ofsaid first and second radiation sensing means whereby the output signalfrom said electrical circuit is nulled upon application of identicalnon-flickering radiation to said first and second radiation sensingmeans.

6. A flame monitoring system as set forth in claim 5, including:

means for enclosing said first and second radiation sensing means, saidenclosing means including a lens and deflecting means for focusingradiation to said first and second radiation sensing means in a mannersuch that said first radiation sensing means only receives radiationfrom a part of said region of the flame not received by said secondradiation sensing means and said second radiation sensing means onlyreceives radiation from a part of said region of the flame not receivedby said first radiation sensing means.

7. A flame monitoring system as set forth in claim 6 wherein said meansfor enclosing includes an individual enclosure for each of said firstand second radiation sensing means, each individual enclosure having alens for focusing radiation to the respective radiation sensing meanstherewithin.

8. A flame monitoring syst em as set forth in claim 7 including:

a sighting tube leading from the region of the flame exhibitingflickering radiation to said lens of said enclosing means.

9. A flame monitoring system comprising:

first means, aligned to sense the radiation from a region of a flameexhibiting high frequency flickering radiation, for producing a firstelectrical signal indicative thereof;

second means, aligned to sense radiation from another part of saidregion of said flame exhibiting high frequency flickering radiation, forproducing a second electrical signal indicative thereof;

electrical circuit means for producing anoutput signal which is afunction of the difference between the signals from said first andsecond radiation sensing means;

said electrical circuit further comprising filtering, amplifying, andrectifying means for modifying the output signal of said electricalcircuit means to a form capable of controlling said flame; and,

further including a plurality of pairs of radiation sensing means andeach said pair sighting a different region of said flame exhibitingflickering radiation, each said pair connected to said electricalcircuit so that the output of each said pair of radiation sensing meansis a function of the difference of the individual radiation sensingmeans of said pair with the output signal of said electrical circuitbeing a function of the sum of the outputs of said plurality of pairs ofradiation sensing means.

10. A flame monitoring system comprising:

first means, aligned to sense the radiationfrom a region of a flameexhibiting high frequency flickering radiation, for producing a firstelectrical signal indicative thereof;

second means, aligned to sense radiation from another part of saidregion of said flame exhibiting high frequency flickering radiation, forproducing a second electrical signal indicative thereof;

electrical circuit means for producing an output signal which is afunction of the difference between the signals from said first andsecond radiation sensing means;

said electrical circuit further comprising filtering, amplifying, andrectifying means for modifying the output signal of said electricalcircuit means to a form capable of controlling said flame; and,

further including a plurality of pairs of radiation sensing means andeach of said pairs sighting a region of a different flame exhibitinghigh frequency flickering radiation, each said pair connected to saidelectrical circuit means sothat the output signal of each said pair ofradiation sensing means is a function of the difference of theindividual radiation sensing means with the output signal of saidelectrical circuit means being a function of the sum of the outputs ofsaid plurality of pairs of radiation sensing means.

11. A method for monitoring a flame characterized by random highfrequency flickering radiation components and other radiation componentscomprising the steps of:

sensing the radiation from one part of a region of the flame exhibitingthe random high frequency flickering radiation and generating a firstelectrical signal proportional to the flame radiation; simultaneouslysensing the radiation from a second part of said region exhibiting therandom high frequency flickering radiation components and otherradiation components and generating a wi l.

1. A flame monitoring system comprising: first means, aligned to sensethe radiation from a region of the flame exhibiting high frequencyrandom flickering radiation components and other radiation components,for producing a first electrical signal indicative thereof; secondmeans, aligned to sense radiation from another part of said region ofthe flame exhibiting high frequency random flickering radiationcomponents and other radiation components, for producing a secondelectrical signal indicative thereof; and, electrical circuit means forcombining said first and said second electrical signals to cancel theother radiation components of said signals and retain the random highfrequency flickering radiation components of the signals proportional tothe sensed radiation.
 2. A flame monitoring system as set forth in claim1 wherein said electrical circuit includes; filtering, amplifying, andrectifying means for modifying the output signal of said electricalcircuit means to a form capable of controlling said flame.
 3. A flamemonitoring system as set forth in claim 2 wherein said first and secondradiation sensing means are photovoltaic cells and are connected inseries opposition in said electrical circuit.
 4. A flame monitoringsystem as set forth in claim 2 where said first and second radiationsensing means are photoresistive cells and are connected in parallel onindividual arms of a ''''Wheatstone'''' bridge in said electricalcircuit means.
 5. A flame monitoring system as set forth in claim 1,wherein said electrical circuit means includes means for balancing theoutputs of said first and second radiation sensing means whereby theoutput signal from said electrical circuit is nulled upon application ofidentical non-flickering radiation to said first and second radiationsensing means.
 6. A flame monitoring system as set forth in claim 5,including: means for enclosing said first and second radiation sensingmeans, said enclosing means including a lens and deflecting means forfocusing radiation to said first and second radiation sensing means in amanner such that said first radiation sensing means only receivesradiation from a part of said region of the flame not received by saidsecond radiation sensing means and said second radiation sensing meansonly receives radiation from a part of said region of the flame notreceived by said first radiation sensing means.
 7. A flame monitoringsystem as set forth in claim 6 wherein said means for enclosing includesan individual enclosure for each of said first and second radiationsensing means, each individual enclosure having a lens for focusingradiation to the respective radiation sensing means therewithin.
 8. Aflame monitoring system as set forth in claim 7 including: a sightingtube leading from the region of the flame exhibiting flickeringradiation to said lens of said enclosing means.
 9. A flame monitoringsystem comprising: first means, aligned to sense the radiation from aregion of a flame exhibiting high frequency flickering radiation, forproducing a first electrical signal indicative thereof; second means,aligned to sense radiation from another part of said region of saidflame exhibiting high frequency flickering radiation, for producing asecond electrical signal indicative thereof; electrical circuit meansfor producing an output signal which is a function of the differencebetween the signals from said first and second radiation sensing means;said electrical circuit further comprising filtering, amplifying, andrectifying means for modifying the output signal of said electricalcircuit means to a form capable of controlling said flame; and, furtherincluding a plurality of pairs of radiation sensing means and each saidpair sighting a different region of said flame exhibiting flickeringradiation, each said pair connected to said electrical circuit so thatthe output of each said pair of radiation sensing means is a function ofthe difference of the individual radiation sensing means of said pairwith the output signal of said electrical circuit being a function ofthe sum of the outputs of said plurality of pairs of radiation sensingmeans.
 10. A flame monitoring system comprising: first means, aligned tosense the radiation from a region of a flame exhibiting high frequencyflickering radiation, for producing a first electrical signal indicativethereof; second means, aligned to sense radiation from another part ofsaid region of said flame exhibiting high frequency flickeringradiation, for producing a second electrical signal indicative thereof;electrical circuit means for producing an output signal which is afunction of the difference between the signals from said first andsecond radiation sensing means; said electrical circuit furthercomprising filtering, amplifying, and rectifying means for modifying theoutput signal of said electrical circuit means to a form capable ofcontrolling said flame; and, further including a plurality of pairs ofradiation sensing means and each of said pairs sighting a region of adifferent flame exhibiting high frequency flickering radiation, eachsaid pair connected to said electrical circuit means so that the outputsignal of each said pair of radiation sensing means is a function of thedifference of the individual radiation sensing means with the outputsignal of said electrical circuit means being a function of the sum ofthe outputs of said plurality of pairs of radiation sensing means.
 11. Amethod for monitoring a flame characterized by random high frequencyflickering radiation components and other radiation componentscomprising the steps of: sensing the radiation from one part of a regionof the flame exhibiting the random high frequency flickering radiationand generating a first electrical signal proportional to the flameradiation; simultaneously sensing the radiation from a second part ofsaid region exhibiting the random high frequency flickering radiationcomponents and other radiation components and generating a secondelectrical signal proportional to said radiation; and, combining saidfirst and said second electrical signals to cancel the other radiationcomponents of said signals and retain the random high frequencyflickering radiation components of the signals proportional to thesensed radiation.